Re: [PATCH v2 bpf-next 17/17] sleftests/bpf: add map linking selftest

[Yonghong Song <yhs@fb.com>]

On 4/16/21 1:24 PM, Andrii Nakryiko wrote:
> Add selftest validating various aspects of statically linking BTF-defined map
> definitions. Legacy map definitions do not support extern resolution between
> object files. Some of the aspects validated:
>    - correct resolution of extern maps against concrete map definitions;
>    - extern maps can currently only specify map type and key/value size and/or
>      type information;
>    - weak concrete map definitions are resolved properly.
> 
> Static map definitions are not yet supported by libbpf, so they are not
> explicitly tested, though manual testing showes that BPF linker handles them
> properly.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Ack with a nit below.
Acked-by: Yonghong Song <yhs@fb.com>

> ---
>   tools/testing/selftests/bpf/Makefile          |  4 +-
>   .../selftests/bpf/prog_tests/linked_maps.c    | 30 +++++++
>   .../selftests/bpf/progs/linked_maps1.c        | 82 +++++++++++++++++++
>   .../selftests/bpf/progs/linked_maps2.c        | 76 +++++++++++++++++
>   4 files changed, 191 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_maps.c
>   create mode 100644 tools/testing/selftests/bpf/progs/linked_maps1.c
>   create mode 100644 tools/testing/selftests/bpf/progs/linked_maps2.c
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index d8f176b55c01..9c031db16b25 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -308,11 +308,13 @@ endef
>   
>   SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
>   
> -LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h linked_vars.skel.h
> +LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h		\
> +		linked_vars.skel.h linked_maps.skel.h
>   
>   test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
>   linked_funcs.skel.h-deps := linked_funcs1.o linked_funcs2.o
>   linked_vars.skel.h-deps := linked_vars1.o linked_vars2.o
> +linked_maps.skel.h-deps := linked_maps1.o linked_maps2.o
>   
>   LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
>   
> diff --git a/tools/testing/selftests/bpf/prog_tests/linked_maps.c b/tools/testing/selftests/bpf/prog_tests/linked_maps.c
> new file mode 100644
> index 000000000000..85dcaaaf2775
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/linked_maps.c
> @@ -0,0 +1,30 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2021 Facebook */
> +
> +#include <test_progs.h>
> +#include <sys/syscall.h>
> +#include "linked_maps.skel.h"
> +
> +void test_linked_maps(void)
> +{
> +	int err;
> +	struct linked_maps *skel;
> +
> +	skel = linked_maps__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "skel_open"))
> +		return;
> +
> +	err = linked_maps__attach(skel);
> +	if (!ASSERT_OK(err, "skel_attach"))
> +		goto cleanup;
> +
> +	/* trigger */
> +	syscall(SYS_getpgid);
> +
> +	ASSERT_EQ(skel->bss->output_first1, 2000, "output_first1");
> +	ASSERT_EQ(skel->bss->output_second1, 2, "output_second1");
> +	ASSERT_EQ(skel->bss->output_weak1, 2, "output_weak1");
> +
> +cleanup:
> +	linked_maps__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/linked_maps1.c b/tools/testing/selftests/bpf/progs/linked_maps1.c
> new file mode 100644
> index 000000000000..2f4bab565e64
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/linked_maps1.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2021 Facebook */
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +struct my_key { long x; };
> +struct my_value { long x; };
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_HASH);
> +	__type(key, struct my_key);
> +	__type(value, struct my_value);
> +	__uint(max_entries, 16);
> +} map1 SEC(".maps");
> +
> + /* Matches map2 definition in linked_maps2.c. Order of the attributes doesn't
> +  * matter.
> +  */
> +typedef struct {
> +	__uint(max_entries, 8);
> +	__type(key, int);
> +	__type(value, int);
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +} map2_t;
> +
> +extern map2_t map2 SEC(".maps");
> +
> +/* This should be the winning map definition, but we have no way of verifying,
> + * so we just make sure that it links and works without errors
> + */

If in debug output, you output something like
    map_weak in obj linked_maps1.o wins
you can open debug mode for this test, capture debug output and check 
the above substring. But this is really fragile and not really 
recommended. So as long as functionality works, we should be fine.

> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__type(key, int);
> +	__type(value, int);
> +	__uint(max_entries, 16);
> +} map_weak __weak SEC(".maps");
> +
> +int output_first1 = 0;
> +int output_second1 = 0;
> +int output_weak1 = 0;
> +
[...]